Muffle furnace and method of operating the same



April 1, 1930.

W. W. KEMP MUFFLE FURNACE AND METHOD OF OPERATING THE SAME Filed Aug. 29, 1927 2 Sheets-Sheet 1 April 1, 1930. w. w. KEMP 1,752,800

MUFFLE FURNACE AND METHOD OF OPERATING THE SAME Filed Aug. 29, 1927 2 Sheets-Sheet 2 o m h! Ill/IIJlV/ll/l/l/l/Jl? 7 T/ m 'g J VQM M% W I 1 Z vi g %z4w%/;

Patented Apr. 1 1930 UNITED STATES PATENT OFFICE WILLIAM wALLAcn KEMP, or BALTIMORE, MARYLAND, ASSIGNOR To THE 0. ,M. K P MFG. co., OF BALTIMORE, MARYLAND, A CORPORATION OF MARYLAND Application filed August 29, 1927. Serial No. 216,313.

The present invention relates to improvements in mufile furnaces and method of operating the same. One of the primary objects of the-invention is toprovide for excluding 5 from the interior of the muflle of such a furnace, gases generated in the furnace and further to utilize some of the waste heat of the combustion gases for heating the interior of the mufile. v 7

As the invention is particularly applicable for use with continuously fired furnaces for enameling cast iron or steel bodies in which the muflie is heated by gas, such an embodiment is illustrated in the accompanying drawings, but the invention is not to be understood as being thereby, in its broader aspects, limited to a furnace for this particular character of work or of the gas heated type.

In furnaces of the type referred to, the mufiles are commonly made of refractories and it is a matter ofconsiderable difficulty,

and expense, to prevent the introduction into the muflie, through the more or less porous walls, ofv gases from'the combustion chamber of the furnace. a 1 v In, porcelain enameling furnaces such gases, particularly the carbon dioxide content thereof, have a deleterious effect on the enamel causing a pitting or roughing of the enameled surface 'andpreventlng obtaining the desired smoothness. r I V h To avoid this objection, it has been proposed to'cause such aFs'tack pullor draft 7 through-the combustion chamber of the furnace as to actually produce a slight vacuum in that chamber. This has operated to draw cold air from the surrounding'atmosphere into the mufile, the. back wall of which is' fre;

quently the back wall of the furnace, or

40; through the slight space or crevice which is generally present about the edges of the muffle door. A A

The result of this operation, is that the amount of fuel which must be consumed 1n 4? order to maintain the interior ofthe muffle at the desired temperature isrelatively large; and there is a very considerable waste of high temperature gases through the furnace stackr Again, the cold air which isdrawn into the muflle, as above referred to, is heated therein and drawn outward through the walls thereof into the combustion chamber or furnace. The heat which is acquired by this air is that which has been produced by radiation from the inside of the mufile walls, and is, therefore, relatively expensive. v Q

. By the present invention, means are provided whereby afurnace of thetype referred to may be operated witha relatively small amount of fuel, and, in which a maximum amount of the heat generated in the combustion chamberwill be utilizedso that the operation of the improved furnace will be relatively considerably less expensive than that incident to operating furnaces of the same general type, ascommonly constructed The invention will now be described more in detail in connection with the accompanying drawings, in which Figure 1 is a longitudinalvertical section and partial side elevationfl of" a gas fired enamelingf furnace embodying the present invention, Figure 2 is a transverse vertical section, substantially on the line.2.f2'of Figure 1. Figure 3 is a plan view. 7 A Figure 4 is asection substantially on the line l 4ofF igure1 2. V r i In the drawings, it will be understoodthat the parts are shown more or less convention: ally and diagrammatically,and there can, of

course, be considerable variation from some fired enamelingfurnace which, as shown,'is

provided with suitable bottom, sideand top walls,the side and top walls being enclosed by an outer wall or casing 2.

Within the combustion chamber 1 is supported a suitable refractories muffle 3. As shown, the bottom of the muflle rests upon piers or columns at spaced longitudinally of the combustion chamber so as not to interfere materially with the flow of gases from the tion chamber 1 extends completely around the muflle, the top and side walls of the latter being relatively closer to the adjacent walls of the furnace than the distance separating the bottom of the muffle from the bottom of the combustionchamber.

The combustion chamber communicates through passages 7 formed in the arched top ofthe inner furnace Wall with a fine 8, that extends longitudinally of the furnace and communicates at one end with the stack 9 through which the waste products of combustion from the furnace escape.

The burners 5 are arranged in two groups at opposite sides of the furnace, the members of each group being connected to a suitable manifold "10 which, in turn, is connected to a branch main or supplypipell.

The joint 12 between each manifold l0 and its supply pipe ll is of such nature that the burners may be swung outward away from the furnace wall as a unit (turning about'the axis of the manifold 10) when the furnace is. shut down as represented in dotted lines in Figure 2. This arrangement permits the burners to be positioned relatively remote from the walls of the furnace when notin use so that they are not subjected tothe radiated heat from the furnace chamber and the life of the burners is thereby lengthened. According to the present invention, means are provided for'preventing the gases of the products of combustion entering the muffle 3 and affecting thearticles being treated therein. Such means in the embodiment of the invention illustrated, comprise ablower 20 which, through a pipe 21, is connected with} a recuperator 22 located in the furnace stack 9. The recuperator connects the pipe 21 witha conduit or pipe 23 that extends longitudinally of the furnace duct 8, and is provided with depending outlet branches 24; that extend through the ducts 7 and the top of the muflle 3 into the interior of the latter.

According to the invention, the blower 20 is operated to force air through the conduits 21, 23 and the interposed recuperator, so that the same is delivered into the muffle 3 at a pressure not less than that produced by the combustion in the furnace combustion chamber. This air, it will be noted, is preheated in passing through the recuperator 22, the stack 9 and the duct 8 so that it enters the muffle at a sufficient temperature to prevent withdrawing any particular amount of heatfrom the walls of the muffle.

Asabove stated, the air is supplied to the muflie under a pressure sufficient to overcome the pressure in the combustion chamber, and will thus prevent combustion gases from entering the muflle. According to the present invention, the combustion gases will be maintained in the furnace under slight pressure, instead of under a partial vacuum as has been the common practice heretofore with furnaces ofthe same type. This pressure within the furnace can be maintained and regulated by a damper 25 located in the stack 9.

The blower 20 is represented as being located on top of the furnace in the drawings, but it will be understood that this is not a feature of the invention and is merely shown in order that the illustration of the entire apparatus may be complete. The blower may be of any suitable type and supported in any desired relation to the furnace. Preferably it would probably be located some distance from the furnace. The capacity of the blower is designed to be such that it will always supply an amount of air in excess of that which is required to be admitted to the muffle.

A suitable blow-0E valve 21 is provided in the pipe 21, and between this valve and the recuperator 22 is arranged an index cook 21?, bymeans of which, the volume of air passingthrough the recuperator-may be varied andregulated as desired. J

In manipulating the furnace, itv will prob ablybe preferable to provide two pressure gauges, indicating respectively the pressures in the furnace chamber about the muflie and the pressure within the latter. By observing these two gauges, an operator can properly manipulate the index cock 21 so thatethe pressure within the mufi'le' will not be less than that in the combustion chamber.

While the embodiment of the invention illustrated is described as including gas burners, it will be appreciated that it is not limited to furnaces in which this particular heating medium is employed. Oil or other c0mbustibles may be substituted if desired, and the apparatus and method described will effectually prevent gases from the combustion chamber gaining access to the interior of the muffle eitherthrough the more or less porous walls thereof, orthroughcracks or crevices that may exist between the walls, door, etc., of the muffle.

Access to the interior of the muffle 3 is had through an opening in the front wall of the furnace controlled by a suitable door 26. This, in the embodiment of the invention illustrated, is designed to be a sliding door, the inner face thereof and the corresponding wall being inc-lined slightly downward toward the bottom of the furnace. Such door may be of any suitable character. 7

It is believed that the operation of the improvements and advantages thereof will be readily appreciated from the foregoing description.

By supplying air pressure to the interior of the muffle 3, it is possible to effectually prevent any of the gases from the furnace combustion chamber 1 entering the mufiie, and as such air is preheated the mufiie walls are not chilled and reduced in temperature as has been the case in furnaces of the same type as commonly constructed. By the invention, it is possible to maintain the gases in the combustion chamber of the furnace under slight pressure instead of a vacuum and thereby effeet a material reduction in the amount of gas required to properly heat the muffle.

What I claim is 1. The herein described method of operating muffle furnaces including a combustion chamber and a refractories mufiie comprising maintaining pressure in both the combustion chamber and muflle, the pressure within the muffle being such as to prevent the admission thereto of gases from the combustion chamber, for the purpose described.

2. The herein described method of operating muffle furnaces including a combustion chamber and a refractories mufiie, comprising heating the mufiie by passing through the combustion chamber heated gases under pressure, and maintaining within the muflie a pressure not less than that of the gases in the combustion chamber, whereby said gases will be prevented from entering the muffle, for the purpose described.

3. In a muffle furnace, the combination with a combustion chamber and a refractories muffle adapted to be heated by the combustion gases in said chamber, of means for maintaining pressure in the combustion chamber, and means for maintaining within the mufile pressure suflicient to prevent admission thereto of. gases from the combustion chamber.

4.. In a muffle furnace, the combination with r a combustion chamber and a refractories muffle adapted to be heated by the combustion gases in said chamber, of means for maintaining pressure in the combustion chamber, and means for supplying air to the mufiie and maintaining it under sufficient pressure to prevent the admission thereto of gases from the combustion chamber. 7

5. In a muiflv furnace, the combination with a combustion chamber and a refractories muflie adapted to be heated by the combustion gases'in said chamber, of means for maintaining pressure onthe gases in the combustion chamber, and means for supplyinfg air to themufileundera pressure suflicient to prevent gases from the combustion chamberpassing t'o the interior of the 'mufile. '36. In a'mufiie furnace, the combinationof a'refractories muffle, means for eXteriorly. heating the'muffle by combustion of gas .un-. der pressure, and means communicating with the interior of the mufiie and adapted to maintain therein a pressure suflicient to prevent the admission thereto of any of theheating gases. i f

7. In a muffle furnace, the combination of a refractories muflle, a combustion chamber for heating the muflie, a conduit communicating with the interior of the muflie and exposed outside thereof to the heat of products of combustion passing from said chamber, and a blower connected with said conduit, for the purpose described.

8. In a muffle furnace, the combination of a combustion chamber, a mufiie within said chamber, means for supplying air under pressure to the interior of the mufiie to prevent combustion products from entering the muffie, and means for preheating the air supplied to the interior of themuflle.

9. In a furnace of the type referred to, the combination of a furnace, a muflie within the combustion chamber of the furnace, a conduit exposed to the heat generated in the combustion chamber and provided with a plurality of branches opening into the mufi'le, andmeans for forcing air through said conduit under a pressure as great as that produced in the combustion chamber, for the purpose described. I

10. In a furnace of the type referred to, the combination of a combustion chamber, a muffle within said combustion chamber, a plu- 'rality of burners for heating the muffle, a

from the combustion chamber, a conduit connecting the recuperator within the interior I of the muffle, and means for forcing air through the. recuperator' and said conduit under a pressure as great as that produced in the combustion chamber.

12. In an enameling furnace of the type referred to, the combination of a furnace h'aV- t ing a combustion'chamber opposite side walls of which are each providedwith a plurality of openings for burners; a refractories muf-t fle within said: combustion chamber, a;b\j1rner" within each of the said burner-openings in the walls ofthe furnace, means f rIsupp1yingvfuel to the burners, and means for sup- 1 I plyingair to the interior of the muffle under a pressure as great as that produced in the combustion chamber by the products of combustion ofthe burners. t v

In testimony whereof I have hereunto set myi hand. a 1 t tt i a WILLIAM WALLACE KEMP. 

